The basic objective of the research is to investigate the control of mammalian visual sensitivity. Using recordings from axons of single retinal ganglion cells in the rat's optic tract, we will explore retinal mechanisms involved in the pooling of light adaptation and the pooling of signals from bleached photoreceptors. We will investigate the control of sensitivity in the receptive field center of ganglion cells. We will investigate the nature and extent of the contributions from the ganglion cell's center and surround mechanisms to the control of sensitivity under light-adapted and dark-adapted conditions. The pupil constricts in response to light stimulation of the retina, thus protecting visual pigments from bleaching and contributing to the enhancement of visual sensitivity. The neural pathway responsible for the pupillary light reflex is not well understood. We will record single cell activity from the pretectum (pretectal olivary nucleus and nucleus of the optic tract) and the Nucleus of Edinger-Westphal in the pupillary light reflex pathway. We will simultaneously record and analyze the changes in pupil size which will be correlated to cell activity in these nuclei. In addition, suspected pupillomoter areas will be stimulated while pupillary movements are recorded to estimate the effectiveness of a given site in driving the pupil. From a given site, we will attempt antidromic activation of cells in lower parts of the pupil pathway. Such activation will confirm functional connections between the sites in the pupillary light reflex pathway.